1. Field of the Invention
The present invention broadly relates to sheet shaped heat generating bodies, particularly to such thin and flexible heat generating sheets which reduce displacement and concentrate placement of heat generating composition, and the manufacturing method thereof
2. Related Art
Heat generators which have as their main component oxidizable metals such as iron powder are widely used as pocket heaters, wherein the heat generating composition which contacts with oxygen in the air to emit heat is packed in air permeable bags.
Although these kinds of heat generators are advantageous in that they may be used in a simple manner, they have problems in that when wearing the generator on the body, the heat generating composition moves down to the bottom of the bag due to its weight, not only during sports but also when standing still, so that the change of shape causes an uncomfortable feeling to the wearer and the heat generating feature becomes less effective.
Various efforts have been made to hold the heat generating composition in or between supporting members to form a sheet-like product as a means for reducing these defects. Described below are examples of such efforts:
a) A method of holding the heat generating composition with wire mesh or net shaped plastic objects (Patent Laid-Open Sho 53 (1978)-84246 Publication); PA1 b) A method of superposing metal foils such as aluminum foils on non-woven fabric made of activated carbon fiber and impregnated with chloride, water or other oxidation auxiliary agents (Patent Laid-Open Sho 63 (1988)-37181 Publication); PA1 c) A method of spraying a heat generating agent on Japanese paper impregnated with an oxidation auxiliary agent, and thereafter subjecting it to pressure to mold such product into a sheet-like shape (Utility Model Sho 64 (1989)-42018 Publication); PA1 d) A method of laying one over the other a plurality of non-woven fabrics made of heat-fused fibers which may include plant fibers, and then distributing chemical heat generating agent therein (Patent Laid-Open Hei 2 (1990)-142561 Publication); and PA1 e) A method of distributing heat generating agent on a supporting sheet which comprises unevenly layered fibers with a large number of very fine pores, and to hold the agent thereon (Patent Laid-Open Hei 3 (1991)-152894 Publication). PA1 a) When holding the generator with wire mesh or net shaped plastic objects, the sheet-like product becomes more rigid and is impractical for use, and the heat generating composition powder becomes easily detached. PA1 b) In products made by superposing metal foils such as aluminum foils on non-woven fabric made of activated carbon fibers, etc. impregnated with oxidation auxiliary agents, the metal surface area is considerably small in comparison to products using metal powders, such that a good heat generating effect cannot be achieved. If the number of foils is increased, this results in reducing the flexibility of the product. PA1 c) In products made by spraying the heat generating agent on paper which is then subjected to pressure to form a sheet, the heat generating agent comes off through folding or shaking, which is not practical. PA1 d) The combination of a plurality of non-woven fabrics by utilizing the water holding property of plant fibers and the heat fusion of synthetic fibers not only renders the structure and processing complicated, but also has practical problems in that the sheet-like object lacks flexibility due to instances where the non-woven fabrics do not adhere to each other, depending on the type and blending ratio of the heat fusive fibers and due to the rigid net-like structure in heat fusion. PA1 e) Concerning the method of distributing heat generating compositions on the supporting sheet made of irregularly layered fibers with a large number of very fine pores, this is a good method in that the composition may be distributed and held inside the pores in a homogenous manner. However, due to the fact that after securing the iron powder, a suspension liquid containing activated carbon, etc. is sprayed, it is difficult to hold the heat generating composition as a whole in a homogenous mixture.
Technical Problems to be Solved by the Invention
However, the related art described above has the following problems in the manufacturing process of the heat generating sheet or the resulting heat generator.
As shown above, it is strongly desired to develop a flexible heat generating body, wherein the heat generating sheet is manufactured so as to allow easy and homogenous distribution and holding of the heat generating composition while preventing leakage of the powder, and a method of manufacturing the same.